1. Field of the Invention
This invention relates to a pattern design method for forming lithography contact/hole (hereinafter referred to as a xe2x80x9cC/Hxe2x80x9d) pattern, especially to form a C/H pattern with preferred depth of focus.
2. Description of the Related Art
In a typical semiconductor process, a contact/hole (hereinafter referred to as a xe2x80x9cC/Hxe2x80x9d) is formed by a C/H pattern formed on a semiconductor layer through exposure and development steps.
FIG. 1A is a schematic diagram illustrating the C/Hs formed by exposing with a ⅔ annular filter of an off-axis illumination system. FIG. 1B is a graph of the Critical Dimension (hereinafter referred to as a CD) to Depth of focus (hereinafter referred to as a DOF) curve after exposure by the ⅔ annular filter of the off-axis illumination system. Comparing FIGS. 1A and 1B, when a C/H has a dimension approximate to 105 nmxc2x110 nm, its DOF is about 0.2 xcexcm.
The higher resolution (i.e., the smaller line width) makes the shallower DOF when introducing the sub-micrometer process in lithography. Accordingly, the concurrent increase of resolution and depth of focus has become a research issue.
Accordingly, an object of the invention is to provide an assist pattern design method for lithography C/H process, to increase the depth of focus without lowering the resolution.
The pattern design method for lithography C/H process of the present invention includes the following steps: determining the exposure wavelength of a lithography machine light source; determining a minimum resolution line width by the sigma, process integration parameter and numerical aperture of the lithography machine; recovering the minimum line width on a mask according to the miniature scale of the determined minimum resolution line width; and using a line pattern smaller than the recovered minimum line width to connect multiple C/H patterns on the mask.
A characteristic of the present invention is the minimum resolution line width W complying with the equation:       W    =                  k        xc3x97        λ                              (                      1            +            σ                    )                xc3x97                  N          .          A          .                      ,
where, k is the process integration parameter; xcex is the exposure wavelength of the lithography machine light source; "sgr" is the sigma of the lithography machine; and N.A. is the numerical aperture of the optical projection system in the lithography machine (i.e., stepper).
According to the method of the present invention, the depth of focus is increased when exposing the C/Hs.
Furthermore, according to the method of the present invention, the optical proximity effect is corrected.